1. Field of the Invention
The present invention relates to an image communication apparatus including a transmitting device for transmitting an image signal, and a receiving device for receiving an image signal which has been transmitted by the transmitting device.
The present application claims priority of Japanese patent application No. 2008-25655, filed on Feb. 5, 2008, and Japanese patent application No. 2009-6597, filed on Jan. 15, 2009, and the contents of which are incorporated herein by reference.
2. Description of the Related Art
In systems for transmitting and receiving images by wireless, a communication state is changed depending upon the peripheral environment so that a data amount which can be transmitted for unit time varies. In the case where the communication state is deteriorated by the peripheral environment, an error rate of data being transmitted by wireless becomes high so that display of an image based on the data becomes difficult to see. In the Japanese Patent Application, First Publication No. 2002-325074, in order to solve the above-mentioned problem, there is described a technology to perform disposal processing of received data having a high error rate due to deterioration of the communication state to request re-sending of data for the transmitting side so that throughput corresponding to the wireless communication system can be obtained. On the other hand, there is generally carried out an approach to transfer a picked up image as compressed data such as JPEG, etc. in order to shorten the communication time to suppress power consumption in the case of transmitting/receiving image data.
In the technology described in the Japanese Patent Application, First Publication No. 2002-325074, there is employed a configuration to calculate, every frame, an error rate of received image data to perform disposal processing of image data of a corresponding frame in the case where the error rate is a predetermined threshold value or more, and to save image data of one frame into buffer in the case where the error rate is less than the predetermined threshold value, and to display an image on a display unit. Moreover, in the case where disposal processing of image data is performed at a certain frame in order to obtain a desired performance, the image is displayed on the basis of image data of the previous frame saved in buffer. For this reason, in the case where the communication state continues to deteriorate, a display picture is placed in freeze state because image data of the previous frame is used for display at all time. As a result, it becomes impossible to visually recognize images picked up on the real time basis.
On the other hand, in the technology for transferring a picked up image as compressed data such as JPEG, etc., when any error takes place during transfer of compressed data, there are many cases where data undergoes a large amount of damage as an image. As a result, it is required to transfer all data in the state where no error exists. For this reason, there is used a technology to perform transfer of image data in the state divided into small blocks to resend data on a block basis at the time of occurrence of an error. However, in the case where the communication state is deteriorated, the number of packets for which re-transfer is required becomes large, and an error may take place even with re-sending. When the 2nd and 3rd re-transfer operations are sequentially performed, since a time required for transmitting one picture is limited, there are instances where image transfer of one picture is not completed within a predetermined time.